oldboy
nounUK /ˈəʊld.bɔɪ/
US /ˈoʊld.bɔɪ/
An oldboy is a grown-up man who used to go to a certain school.
My dad is an oldboy of the school down the road.
OTHER MEANINGS
2. A friendly way to call an older man or a pal.
Thanks for the help, old boy!
3. An old man, sometimes said in a joking way.
The old boy next door always waves at us.
4. A former member of a sports team or club.
He is an oldboy of the local rugby club.